Method and System for Using a Target Gas Provided by a Gas Decomposition Device

ABSTRACT

The present invention relates to a method for utilising a target gas flow consisting of pressurised target gas, which is provided by a continuously-operated gas decomposition device, wherein the target gas flow is supplied to a target load which discontinuously decreases the target gas flow, so that occasionally an excess target gas flow that is not decreased by the target load accrues, as well as a system for supplying a target load. The excess target gases occurring in a gas decomposition device and optionally additionally resulting waste gases may be used in a resource-saving manner through the method and the system according to the invention. This is achieved by the excess target gas flow being supplied as a propellant gas to a compressor which compresses another gas and supplies it as a compressed gas in a compressed gas line, via which it is fed to another load.

The invention relates to a method for using a target gas flow consistingof pressurised target gas, which is supplied by a continuously-operatedgas decomposition device, wherein the target gas flow is supplied to atarget load, which discontinuously decreases the target gas flow, sothat an excess target gas flow that has not been decreased by the targetload occasionally accrues.

Likewise, the invention relates to a system for supplying a target loadwith a pressurised target gas flow and another load with anothercompressed gas. In this case, the system comprises a gas decompositiondevice which provides a target gas flow for a target load whichdiscontinuously decreases this target gas flow, so that an excess targetgas flow accrues in the gas decomposition device. Furthermore, such asystem comprises a compressed gas operated compressor to compress andfeed the compressed gas into a compressed gas line leading to the otherload.

In a gas decomposition device a gas mixture is separated into a targetgas and an exhaust gas. An example of such a gas decomposition device isan Air Separation Unit (ASU) for air separation. Such air separationunits separate the ambient air into its main components of nitrogen andoxygen. Depending on the field of application, however, such airseparation units may also extract argon or other noble gases from theambient air.

On an industrial scale, air separation units are used which operate onthe basis of so-called cryogenic distillation or low-temperaturedistillation (“Linde method”). This method delivers pressurised oxygenas the target gas. In addition, a gas flow which contains theatmospheric nitrogen and the other gases which are not separated in therespective separation process and which are contained in the air, isobtained as the “waste gas” of the oxygen production process.

Devices of this type are used, for example, in the field of productionof iron or steel melts, but also in many other processes in which pureoxygen is required in larger quantities. Thus, for example, for theso-called “carbon drop” oxygen is blown onto or into the respective meltto eliminate the carbon content or unwanted iron companions from themelt by oxidation.

A fundamental problem with gas decomposition devices of the typeconsidered here is that they are generally operated continuously,because high energy and time costs are incurred at the start-up of suchdevices. Gas decomposition devices therefore continuously produce anoptimally constant target gas flow. This is subjected to high pressureupon leaving the gas decomposition device.

Opposing the continuous provision of the target gas flow is a usuallydiscontinuous demand, i.e. a demand that varies over time on the part ofthe target load. In fact, the temporarily not, or not completely, excesstarget gas flow may be temporarily stored in buffers in order to be keptready for demand peaks. However, the cost of such an intermediatestorage and the associated energy losses are considerable.

Various proposals are known for the valuable use of excess target gasand waste gas flows in continuously-operated gas decomposition devicesin terms of resource conservation.

An example of these proposals is the integration of an air separationunit into a pig iron production process as described in US 2012/0032378A1. In this process, the air separation unit provides oxygen for blowinginto a blast furnace. The excess oxygen flow temporarily not, or onlypartially, decreased by the blast furnace is fed into a steam generatorin order to improve the efficiency of the combustion of the processgases resulting from the production of pig iron conducted for thegeneration of the required heat. At the same time, the pressurisednitrogen arising as a waste gas in the air separation process issupplied, on the one hand, to a coal injection device, while, on theother hand, it is used to support the driving of a gas turbine whichdrives a generator for generating electrical energy.

Against the background of the above-described prior art, the object hasarisen to propose a simplified method suitable for wider use and asimilarly designed system, with which the excess target gases and wastegases optionally additionally generated in a gas decomposition devicemay be used in a resource-saving manner.

The invention achieves this object through the method specified in claim1 and the system proposed in claim 9.

Advantageous embodiments of the invention are specified in the dependentclaims and are explained in detail below as is the general inventiveconcept.

The method according to the invention for utilising a target gas flowconsisting of pressurised target gas, similar to the prior art explainedat the outset, assumes that the target gas flow is provided by acontinuously-operated gas decomposition device. However, a target loadsupplied with the target gas flow decreases this target gas flow onlydiscontinuously, so that at times an excess target gas flow that has notbeen decreased by the target load, is obtained.

According to the invention, the excess target gas flow is now fed as apropellant gas to a compressor which compresses another gas and feeds itas compressed gas into a compressed gas line via which it is fed toanother load.

Thus, according to the invention, the drive side of a compressor, whichcompresses “another gas” that is different from the target gas flow, andfeeds it into a general compressed gas line, is supplied with the excesstarget gas flow. “Excess” here relates to both the case in which thetarget load does not decrease any target gas from the gas decompositiondevice, so that the excess target gas flow is equal to the target gasflow provided by the gas decomposition device, as well as the case whereonly a reduced amount of the target gas flow is decreased by the targetload, so that only a partial flow of the target gas flow provided by thegas decomposition device is obtained as an excess target gas flow.

In a corresponding manner, a system according to the invention whichsupplies a target load with a pressurised target gas flow and anotherload with a different compressed gas, comprises a gas decompositiondevice which provides a target gas flow for a target loaddiscontinuously decreasing this target gas flow, so that an excesstarget gas flow is produced in the gas decomposition device, and acompressed gas operated compressor for compressing and feeding thecompressed gas into a compressed gas line leading to the other load.According to the invention, in such a system, the compressor isconnected on the drive side through a propellant gas line to an outletof the gas decomposition device, via which outlet the excess target gasflow flows as a propellant gas to a propellant gas connection of thecompressor.

The high pressure excess target gas flow provided by the gasdecomposition device is thus effectively used to generate a compressedgas that is required elsewhere, for example it may be needed in largequantities or at a lower pressure level elsewhere in the respectivesystem network, to which the gas decomposition device and the targetload also belong. The great advantage of this coupling according to theinvention is that the energy stored in the excess target gas flow isused for the compressor, while simultaneously the excess target gas flowis decompressed via the compressor. In this way, the excess target gasflow, depending on the nature of the gas of which it consists, may bedirectly sent for re-use where it is needed at a lower pressure level.

The invention offers a particularly advantageous effect if the excesstarget gas is used not only to drive the compressor, but is alsointroduced into the pressure line fed by the compressor. For thispurpose, the excess target gas flow may be mixed with the other gas tobe compressed by the compressor, or with the compressed gas compressedby the compressor after or upon passing through the compressor.

Depending on the respective pressure level at which the excess targetgas still is when leaving the compressor, or to which the gas to becompressed by the compressor is brought to by the compressor, this maybe done by the target gas being mixed with the gas fed into the gas linein the flow direction downstream of the compressor. This avoids theproblem of the excess target gas flow not being able to be fed directlyinto the compressed gas line usually as a result of the large pressuredifference, as the proportion of the target gas or the resultingpressure increase in the compressed air line would be too great andthere would be a risk of overloading the pressure line system.

Likewise, it is possible to supply the target gas to the suction side ofthe compressor after it has been decompressed via the compressor, sothat it is mixed there with the other gas to be compressed and theresulting gas mixture is compressed by the compressor and fed into thecompressed gas line.

Regardless of whether the admixing of the target gas to the other gas tobe fed into the pressure line takes place upstream of the suction sideor downstream of the pressure side of the compressor, for this purpose asystem according to the invention may comprise a mixing device which isprovided to mix the target gas or waste gas flow to be introduced intothe pressure line with a further gas.

Another way to use the excess target gas flow to compress a gas andsimultaneously feed it into the compressed gas line, consists in thechoice of a compressor in which a drive gas flow, in this case theexcess target gas flow, is fed into the respective compressor in such away that it may be used as a propellant gas on the suction side of thecompressor and accordingly entrain the gas to be compressed and compressthe latter as a result of the pressure difference between the propellantgas and the gas to be compressed. The mixing of excess target gas withthe other gas compressed in the compressor then takes place in thecompressor itself.

The principle of such a gas jet compressor that is suitable for thepurposes according to the invention is described in DE 91 01 135 U1.According to the invention, the compressor has a suction side, a driveside and an outlet side. The suction side is the side of the compressorto which the gas to be compressed is supplied. The outlet side isaccordingly the side of the compressor from which the gas compressed inthe compressor flows out. The drive side of the compressor according tothe invention refers to the side of the compressor via which thepropellant gas is supplied. The compressor therefore has two inletvolume flows: the volume flow on the drive side and on the suction side.The compressor compresses the gas supplied on the suction side as aresult of the pressure difference between the compressed propellant gasand the decompressed gas fitted on the suction side.

The use according to the invention of an excess target gas flowoccurring in a gas decomposition device proves to be particularlyeffective if the gas decomposition device is a conventional airseparation unit which extracts oxygen as the target gas from the ambientair.

In principle, the method according to the invention may be applied toall gas decomposition devices, regardless of whether each of the gasflows obtained through the decomposition is fed to a target load or oneor more of these gas flows is separated during the decomposition processas a waste gas flow for which there is no target load.

In the event that a waste gas flow results from the decompositionprocess, it may be expedient to collect the waste gas in a pressureaccumulator and, if necessary, use this to drive the compressor. In thisway, the waste gas may be used as a buffer for the time when, due to alarge demand by the target load, there is not sufficient excess targetgas flow available for the operation of the compressor. In thisembodiment, the resulting waste gas flow that is generally highpressured as well is thus passed into a pressure accumulator, the wastegas is stored there, and then used when needed to drive the compressor.Another advantage of this embodiment is that due to the accumulator thecompressor may be independent of the air separation process.

For this purpose, in a system according to the invention, an accumulatorthat is connected to an outlet of the gas decomposition device may beprovided for a waste gas arising during the gas decomposition process.

If the waste gas should also be usable for the compression of the othergas, this may be accomplished by additionally connecting the accumulatorto the drive side of the compressor via a supply line and providing avalve which releases the supply line when needed in order to drive thecompressor with the waste gas stored in the accumulator.

Depending on its type and the type of the other gas to be compressed bythe compressor and fed into the compressed gas line, it may also beexpedient to mix the waste gas with the other gas to be compressed bythe compressor, or the compressed gas compressed by the compressor.

In order to allow the mixture of waste gas with the other gas and theexcess target gas optionally added, the accumulator may be connected onthe outlet side to the suction side of the compressor or with thecompressed gas line, in order to, if necessary, mix waste gas in the gasflow to be compressed by the compressor or in the compressed gas flowcompressed by the compressor.

Regardless of where the mixing is done, the admixing of target gas orwaste gas to the other gas proves to be particularly resource-saving.This applies, in particular, if the admixture of target gas and wastegas takes place simultaneously. By setting a certain mixing ratio forthe admixed target and waste gas, the gas mixture formed from targetgas, waste gas and the other gas and fed into the compressed gas line ascompressed gas can offer optimised properties for the respective uses,or may at least be so composed that, despite the admixing of target gasor waste gas, there are at least no negative effects on the one or moreother load(s) that are operated with the compressed gas mixture fed intothe pressure line, and thereby the inherent energy in the target andwaste gas may be used in an optimal way. In a system according to theinvention, the addition of excess target gas and waste gas may be madepossible by the fact that the system comprises a mixing device that isintended to mix a further gas to the target gas flow or waste gas flowthat is to be introduced into the pressure line.

In the case of mixing before or in the compressor, it is of coursepossible to increase the proportions of the admixed target and wastegases in the gas mixture to be compressed by the compressor, so that atleast temporarily, no, or almost no, other gas is needed any longer inorder to produce the compressed gas flow fed into the pressure line.

Likewise, it is of course possible for the one gas, for example only thewaste gas or only the excess target gas, to be admixed before or in thecompressor, while the other gas may be added to the compressed gas afterthe compressor.

The possibility of admixing target or waste gas before, in or after thecompressor is particularly advantageous, when the target gas is oxygenand the other gas to be compressed by the compressor is ambient air, andwhen the waste gas is made up from the other gases contained in theambient air, in particular nitrogen. If only the excess oxygen targetgas flow is to be added to the other gas (ambient air), then the admixedamount of oxygen may be so limited that a possibly critical oxygencontent with respect to corrosion or oxidation of machine and line partsis not exceeded in the compressed gas fed into the pressure line. Atypical limit here may be an oxygen content of 30 vol.-%. If nitrogen isalso added at the same time, it is possible to produce a gas mixturewhich has a composition similar to that of ambient air, wherein here itis also possible to increase the proportion of excess target gas orwaste gas present in each case to an innocuous limit. Another advantageof the, according to the invention, optionally provided admixture ofexcess oxygen target gas or waste gas comprising of nitrogen, andoptionally the other gas constituents of the ambient air is that thecost of particle filtration, drying and oil separation that is customaryin the field of compressed air production, is reduced, since both thewaste gas as well as the target gas have already been subject to theseoperations in the gas decomposition device.

The method according to the invention is explained in more detail belowwith reference to a drawing, wherein:

FIG. 1 schematically shows a system for supplying a target load with apressurised target gas flow and another load with another compressedgas.

FIG. 2 schematically shows a diagram illustrating the components of themethod according to the invention and their interaction.

The system 1 shown in FIG. 1 for supplying a target load and at leastone further load, is constructed as follows:

In the gas decomposition device 2, a highly pressurized target gas flowZ consisting of oxygen is generated from the ambient air U. In thedecomposition process, a waste gas flow A consisting of the remaininggas constituents of the ambient air U, mainly nitrogen, is additionallyseparated in the gas decomposition device 2.

The target gas flow Z generated by the gas decomposition device 2 issupplied to a target load 4 via a supply line 3. However, the targetload 4 decreases the target gas ZG only discontinuously, so that attimes an excess target gas flow Zue is produced in the gas decompositiondevice 2.

The excess target gas flow Zue is guided via a propellant gas line 5 tothe propellant gas inlet 6 of a compressor 7 that is in the form of agas jet compressor. The commercially-available compressor 7 that isdesigned in a manner known per se, comprises a mixing chamber 8 with asuction connection 9 and a nozzle device 10, via which the excess targetgas flow Zue is introduced into the mixing chamber 8. The nozzle device10 is so designed that the discharged excess target gas flow Zue entersthe mixing chamber 8 at high speed, entrains another gas G at thesuction connection 9, and then enters a funnel-shaped compressionchamber 10 a that tapers conically in the flow direction of the excesstarget gas flow Zue entering the mixing chamber 8, in which the gasmixture formed from the target gas flow Zue and the other gas G iscompressed, so that it is fed as compressed gas DG into a compressed gasline 11. If it turns out that the power of the compressor 7 is notsufficient, it may be arranged in series with a conventional compressorwhich carries out the optionally still required final compression of thecompressed gas DG to the respective specified pressure.

The compressed gas line 11 supplies various other loads 12,13,14 withcompressed gas DG. In the event that no excess target gas flow Zuesufficient for the operation of the compressor 7 is available,pressurised gas DG is fed into the compressed gas line 11 via aconventional compressor 15.

The other gas G available at the suction connection 9 of the compressor7, i.e. supplied separately from the excess target gas flow Zue, ismixed from waste gas AG and ambient air U. For this purpose, a mixingdevice 16 connected to the suction connection 9 is provided, that mixesambient air U with a waste gas flow A′ in a specific mixing ratio. Themixing ratio is adjusted as a function of the excess target gas flow Zueguided into the compressor 7, so that, on the one hand, a sufficientlylarge pressure gas flow D enters the compressed gas line 11 and, on theother hand, the compressed gas DG fed into the compressed gas line 11 asa compressed gas flow D comprises an oxygen content, for example,between the oxygen content of normal air and 30 vol.-%. If asufficiently large waste gas flow A′ is available, the amount of admixedambient air U may be reduced to “0%”. Likewise, the oxygen content ofthe compressed gas DG may be set significantly higher if the corrosionresistance of the compressed gas line system 11, through which thepressurised gas DG flows, and the loads 13 which are supplied with thecompressed gas DG, allow this.

The waste gas flow A′ reaches the mixing device 16 via a line 19, whichis connected to an outlet of an accumulator 17. The accumulator 17 isfed by the gas decomposition device 2 with the waste gas flow A via asupply line 18. Another or several further loads 21 may be supplied withthe waste gas AG via a supply line 20 connected to a further outlet ofthe accumulator 17. The gas decomposition device 2 is decoupled from thedrive side of the compressor 7 by the accumulator 17.

FIG. 2 clarifies the sequence of the method according to the invention,implemented, for example, on a system of the type shown in FIG. 1, in ageneral form.

A gas mixture U (ambient air) is separated into compressed target gas ZGand waste gas AG in the gas decomposition device 2.

However, the waste gas AG is not vented unused into the environment, butis buffered in the accumulator 17.

A further load 21 may be supplied with the waste gas AG via theaccumulator 17.

In addition, waste gas AG is supplied from the accumulator 17 to themixing device 16. There, a gas mixture G is adjusted as a function ofthe excess target gas flow Zue introduced into the compressor 7, so thatthe composition of the compressed gas DG fed into the compressed gasline 11 corresponds to a target specification. If the waste gas flow A′present in the mixing device 16 is insufficient, ambient air U may beadded to the waste gas flow A′ in the mixing device 16.

In the compressor 7 the gas mixture G is compressed to the compressedgas DG, which is fed into the compressed gas line 11 as the compressedgas flow D and supplies the other loads 12-14.

If the available excess target gas flow Zue is not sufficient for thegeneration of a sufficiently large compressed gas flow D, compressed gasDG is additionally fed into the compressed gas line 11 via thecompressor 15.

REFERENCE LIST

-   1 System-   2 Gas decomposition device-   3 Supply line-   4 Target load-   5 Propellant gas line-   6 Propellant gas inlet-   7 Compressor (gas jet compressor)-   8 Mixing chamber-   9 Suction connection-   10 Nozzle device-   10 a Compression chamber-   11 Compressed gas line-   12-14 Other loads-   15 Compressor-   16 Mixing device-   17 Accumulator-   18 Supply line-   19 Line-   20 Supply line-   21 Further load(s)-   A Waste gas flow-   A′ Waste gas flow-   AG Waste gas-   D Compressed gas flow-   DG Compressed gas-   G Other gas-   U Ambient air-   Z Target gas flow-   ZG Target gas-   Zue Target gas flow

1. A method for utilising a target gas flow consisting of compressedtarget gas provided from a continuously operated gas decompositiondevice, comprising: using the target gas flow to supply a target load;using the target load to discontinuously decrease the target gas flow;accruing an excess target gas flow that is not decreased by the targetload; supplying the excess target gas flow a propellant gas to acompressor; compressing another gas; and supplying the compressed gas ina compressed gas line which it is fed to another load.
 2. The methodaccording to claim 1, wherein the compressor is a gas jet compressor,comprising a drive side that is supplied with the excess target gasflow.
 3. The method according to claim 1, wherein the target gas isoxygen, which is obtained by the gas decomposition device separatingambient air.
 4. The method according to claim 1, wherein the excesstarget gas flow is mixed with the other gas before, during, or after itscompression.
 5. The method according to claim 1, wherein a waste gasflow results from the generation of the target gas the gas decompositiondevice.
 6. The method according to claim 5, wherein the waste gas flowis fed to a pressure accumulator, the waste gas is stored there, and thewaste gas is used to drive the compressor if necessary.
 7. The methodaccording to claim 5, wherein the waste gas is mixed with the other gasbefore or after compression.
 8. The method according to claim 5, whereinboth the excess target gas and the waste gas are mixed in a certainmixing ratio with the other before or after compression.
 9. A system forsupplying a target load with a compressed target gas flow and anotherload with another compressed gas, comprising: a gas decompositiondevice, which provides a target gas flow to a target load thatdiscontinuously decreases the target gas flow, so that an excess targetgas flow is obtained in the gas decomposition device, and a compressedgas operated compressor for compressing and feeding a compressed gasinto a compressed gas line leading to another load, wherein thecompressor is connected to an outlet of the gas decomposition device ona drive side via a propellant gas line, through which the excess targetgas flow flows as a propellant gas to a propellant gas connection of thecompressor.
 10. The system according to claim 9, wherein the compressoris a gas jet compressor.
 11. The system according to claim 9, furthercomprising an accumulator which is connected to the outlet of the gasdecomposition device for a waste gas arising during the gasdecomposition process.
 12. The system according to claim 11, wherein theaccumulator is connected to the drive side of the compressor via asupply line, and a valve is provided to free the supply line ifnecessary, and drive the compressor by means of the waste gas stored inthe accumulator.
 13. The system according to claim 11, wherein theaccumulator is connected on an outlet side to a suction side of thecompressor or with the compressed gas line in order to mix the waste gasin a gas flow to be compressed by the compressor, or in a compressed gasflow compressed by the compressor.
 14. The system according to claim 9,further comprising a mixing device which is intended to admix a furthergas to the target gas or waste gas flow to be introduced into a pressureline.